You can force a sync by tapping on Sync Now in Settings but you can not increase the upload/download speed. In fact the speed is mostly dictated by the iCloud servers. In the beginning I tried to do multiple transfers at the same time only to find out that iCloud does not like that at all and starts throttling the transfer to a crawl. So now all transfers are sequential.
Errors with iCloud are mostly temporary and caused by the network connection to the iCloud servers. If anything goes wrong just wait a couple of minutes and most errors will resolve itself.